1. Field of the Invention
The present invention relates generally to tractors having a fifth wheel for hauling cargo trailers and, more particularly, to conversion apparatus for adapting such a tractor to carry a truck bed or like body.
2. Description of the Prior Art
Throughout most of the United States, tractor trailer combinations are commonly used to transport large and, usually, very heavy loads over conventional highways. These tractor trailer combinations typically include a ten-wheeled tractor hauling an eight-wheeled cargo trailer. The trailer is usually towed by resting on a large metal plate, commonly called a fifth wheel, mounted onto the chassis of the tractor. This fifth wheel normally has a slot oriented towards the rear of the tractor and a locking mechanism which engages a large pin, called a kingpin, mounted onto the underside of the trailer. When the fifth wheel engages the kingpin, the locking mechanism secures the pin within the slot of the fifth wheel so as to prevent removal of the kingpin while allowing rotational movement between the tractor and the trailer, thus facilitating towing. Standardization of the fifth wheel and kingpin is fairly common in the transport industry, allowing various types of tractors to haul differing trailer configurations.
Quite often tractors are owned by private individuals who broker their hauling services to various businesses. One of the disadvantages of this entrepreneurial industry, however, is a general inability to use the tractors for other than hauling very large trailers. Several attempts have been made to provide an apparatus for adapting a conventional tractor to carry some type of truck bed so that the tractor may be useful for purposes other than hauling trailers. For example, U.S. Pat. No. 4,702,510 to Davis discloses a flat-bed for demountable attachment to the fifth wheel of a conventional tractor. The flatbed is provided with a kingpin to engage the fifth wheel of a tractor and chains are used to secure the flatbed to the tractor chassis. This approach, however, provides a somewhat precarious mounting between the tractor and the truck bed, thus limiting the stability of the combination tractor-truck bed when hauling heavy loads over rough terrain, such as might be encountered at a construction site. Another example of a tractor-conversion apparatus is illustrated in U.S. Pat. No. 4,662,670 to Kemner. In this approach, a pair of rods are welded transversely to the tractor chassis behind the fifth wheel so as to engage a truck bed having a kingpin and a pair of adjustable hangers suspended from the rearward underside of the truck bed. While apparently providing adaptability to a variety of truck beds, this approach balances the load of the truck bed onto only the three supports of the fifth wheel and the two rods welded to the tractor chassis. Thus, this approach also provides an undesirably precarious mounting structure which may not be suitable for hauling small but otherwise heavy loads.
All of the conversion apparatus discussed above suffer from several disadvantages, such as a need for intricate mechanical linkages and an unsatisfactorily precarious attachment between the truck bed and the tractor chassis. The present invention overcomes these disadvantages.